Hair setting processes, including both permanent and straightening, are usually carried out at room temperature. The process typically includes two phases, namely i) reducing covalent disulfide linkages in the keratinous fibres of the hair, thereby rendering the hair deformable without elasticity, the hair typically being wetted by a solution containing a reducing agent and afterwards rolled on curlers (or mechanically straightened), and ii) re-establishment of a network of cross links in the keratinous fibres of the hair by application of a so-called fixer (which usually contains an oxidising agent), thereby rendering the curly or straightened shape "permanent".
For the purpose of breaking the disulfide cross linkages a number of organic reducing agents can be used, including strong bases such as sodium hydroxide. Thioglycolic acid, thioacetic acid and other sulphur-containing compounds are also commonly used.
Among reagents used for the purpose of fixation of the hair, i.e., compounds capable of re-establishing the physico-mechanical properties of the hair by forming disulfide and other cross links between keratin chains, hydrogen peroxide is the most commonly used reagent as hydrogen peroxide reacts rapidly with the keratin --SH groups. Other examples of commonly used oxidising agents are e.g. perborates, bromates, chlorites, iodates, bromates, persulphates and tetrathionates.
In principle, it is possible to use atmospheric oxygen as an oxidising agent. The direct use of atmospheric oxygen, however, suffers from the disadvantage that several hours are required in order to complete the reaction.
The use of hydrogen peroxide (and other oxidising agents) is preferably avoided as e.g. hydrogen peroxide is known to be caustic to the skin and, accordingly, causes an unsatisfactory working environment for e.g. hair dressers. Furthermore, hydrogen peroxide can damage hair.
Thus, there is a need for a method which may replace the use of hydrogen peroxide and other hazardous oxidising agents in re-formation of keratinous fibre cross links. The method should preferably avoid the use of hazardous chemicals and, at the same time, be easily conducted within a reasonable time, ideally within the time normally required for hydrogen peroxide treatment. Traditionally, hair setting (i.e., waving and straightening) and hair dyeing have been considered as two independent processes, each process being carried out individually by means of different techniques.
Permanent hair dyes are durable to sunlight, shampooing and other hair treatments and need only to be refreshed once a month as new hair grows out. With these dyeing systems the dyes are created directly in and on the hair. Small aromatic colourless dye precursors (e.g., p-phenylene-diamine and o-aminophenol) penetrate deep into the hair where the precursors are oxidised by an oxidising agent into coloured polymeric compounds. These coloured compounds are larger than the dye precursors and cannot be washed out of the hair.
Traditionally, H.sub.2 O.sub.2 is used as the oxidising agent, but also as a bleaching agent. Thus, dyeing compositions comprising H.sub.2 O.sub.2 are often referred to as "lightening dyes" due to this lightening effect of H.sub.2 O.sub.2.
The use of H.sub.2 O.sub.2 in dye compositions has some disadvantages as H.sub.2 O.sub.2 damages the hair. Further, oxidative dyeing often requires high pH (normally around pH 9-10), which also inflicts damage on the hair. Consequently, if using dye compositions comprising H.sub.2 O.sub.2, it is not recommendable to dye the hair often.
To overcome the disadvantages of using H.sub.2 O.sub.2 it has been suggested to use oxidation enzymes to replace H.sub.2 O.sub.2.
U.S. Pat. No. 3,251,742 (Revlon) describes a method for dyeing human hair by dye formation in situ (i.e., on the hair). An oxidative enzyme is used for the colour formation reactions at a substantially neutral pH (pH 7-8.5). Laccases, tyrosinases, polyphenolases and catacolases are mentioned as suitable oxidation enzymes.
EP patent No. 504.005 (Perma S.A.) concerns compositions for hair dyeing which do not require the presence of H.sub.2 O.sub.2 (hydrogen peroxide). The compositions comprise an enzyme capable of catalysing the formation of the polymeric dyes and also dye precursors, such as bases and couplers, in a buffer solution wherein the pH of the composition is between 6.5 and 8 and the enzyme has an optimal activity in the same pH range.
A method for enzyme-mediated dyeing of keratinous fibres, such as hair, has been described in WO 97/19999 (Novo Nordisk) and WO 97/19998 (Novo Nordisk).
Canadian patent 67:93913 discloses a composition containing a metal-containing dye for simultaneously permanent waving and dyeing hair. EP patent No. 328816 describes a process for dyeing of waved or relaxed hair using a metal ion-catalyzed hair dyeing composition.
Until now, there has been not a commercially acceptable method for simultaneously performing permanent dyeing and setting of hair. This is because hair that has been reduced as part of a setting treatment (waving or straightening) will be badly damaged by exposure to hydrogen peroxide at concentrations that are used in conventional permanent hair dyeing products.
A commercially relevant method that would allow simultaneous permanent dyeing and setting of hair would be desired by hairdressers and consumers alike. It will give consumers an entirely new wave of options in their hair style choices. It will also increase convenience and efficiency, in addition to decreasing safety hazards, for both hairdressers and consumers.
Accordingly, there is a need for a method which can be used for simultaneous permanent setting and dyeing of keratinous fibres such as hair.
The method of the present invention overcomes this limitation by providing a mild, peroxide-free method of dyeing hair and re-forming cross links in hair after a reducing treatment. As a result, this method allows simultaneous permanent setting and dyeing of hair without causing excessive damage to the hair.